Why does my gearbox seem to have a mind of its own??

Discussion in 'Engine' started by PJayUK, Nov 12, 2008.

  1. PJayUK

    PJayUK Hardcore MB Enthusiast

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    ML320 W163, E320 W210 & Jaguar X300-XJR6
    I had a go at disconnecting my MAF sensor this morning on my way in. Something just doesn't feel right about my car, problem is I haven't driven another SClass to compare it with to know whether there is a problem or not… Its not running lumpy, starts fine and according to the computer returns around 31MPG after start on my run into work. BUT…

    Since its turned colder, it feels like the gearbox has changed to a lower ratio, its still quite smooth although whines a little when pulling away and shifting from 1-2, but has done since I have owned the car. If anything you could say that it feels "sportier" this sounds weird but it seems to pick up faster, stay in lower gear longer before shifting. On the motorway revs seem a little higher and it reminds me of how my previous car a Jaguar XJ8 Sport used to feel when you put the gearbox into Sport mode. De-acceleration, seems quicker as well, revs seem to drop off very quickly, all in all making the car feel a little less smooth than it did before.

    So I have done two things to try and sort this out. Firstly after reading the forums I tried some reset sequence that is supposed to reset the auto box ECU. Something like ignition on, accelerator to floor for 5 seconds, release gas and turn ignition off for 2 minutes. Didn't seem to do anything, not sure if it works on a W220. Then I disconnected the MAF. Car ran noticeably worse (and the Airmatic warning message came on when I first turned it on for some reason!), power was down and the car seemed to be "hunting" on de-acceleration, didn’t like it, so I connected it again after a couple of miles. Much better!

    Perhaps it seems strange that I am worrying about this, most people would probably pay good money for what feels like extra performance, but I don’t like it when things just happen of there own accord as it suggests that something is wrong. And I liked the rather sedate smoothness that I seemed to have before…

    Any ideas?
     
  2. grober

    grober MB Club Veteran

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    Mercedes gearboxes have a upshift delay built in during cold weather to help warm up the catalytic converter. The car holds on to lower gears for longer so doesn't feel so smooth. but acceleration will be better. If things go back to normal once everything warms up you have nothing to worry about.
     
  3. OP
    OP
    PJayUK

    PJayUK Hardcore MB Enthusiast

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    Car:
    ML320 W163, E320 W210 & Jaguar X300-XJR6
    There is no difference once the box has warmed up. Also its not been that cold this week so would this kick in if its say 10 degrees?

    Dodgy sensor maybe??

    Its booked into the local Indi on Friday to have its future (ie. codes!) read!
     
  4. NewMB

    NewMB Hardcore MB Enthusiast

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    The story about "late upshifts" goes back as long as I can remember with MB's auto's.

    Back in 1987 my father bought a new 560SEC that did this, in the middle of the summer. MB told him that it was normal behaviour when the engine were cold, not the weather.
     
  5. OP
    OP
    PJayUK

    PJayUK Hardcore MB Enthusiast

    Messages:
    504
    Joined:
    Oct 6, 2008
    Location:
    Surrey, United Kingdom
    Car:
    ML320 W163, E320 W210 & Jaguar X300-XJR6
    Can anybody shed any light on the speed that which my revs decrease....

    Basically the revs fall away from say 2500rpm to below 1000rpm almost instantly when I pull off the accelerator....

    Makes slowing down feel a bit unncomfortable!
     
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